Elastic and inelastic resonant tunnelling in narrow-band systems: application to transport in minibands of semiconductor superlattices

The authors consider tunnelling in systems with a finite conduction bandwidth. A physical realization of such a system would be a disrupted semiconductor superlattice imbedded in the base of a n-p-n transistor. There it is possible to tune the energy of the incoming injected carriers by changing the emitter to base voltage. Hence the calculated transmission coefficient, weighted with the energy distribution of the injected electrons, bears direct relevance to measured I-V characteristics. The vertical transport in the unperturbed miniband is described with a tight-binding model, and the disruption, which may arise accidentally, or be fabricated by adjusting the growth conditions, is modelled with an additional double barrier. The transmission coefficient displays a resonant behaviour as a function of energy. Further they evaluate the transmission coefficient in the case where the region connecting the two superlattices couples to dispersionless optical phonons. Optical-phonon-related satellite features are identified. Finally, the relation of the calculated effects to recent experiments is analysed